Conventionally, in positron emission tomography (PET) image reconstruction, the lung field is treated as a low-density tissue structure to account for the presence of lung tissue. However, lung tissue and the pulmonary vasculature have significantly different densities (and consequently, different attenuation coefficients). Conventionally, little to no effort has been made to correct for differences in the density between lung tissue and the vasculature. This can result in an incorrect attenuation correction for the 511 keV gamma rays emitted by the PET contrast media. Furthermore, failure to account for the differences in densities of lung tissue and the pulmonary vasculature can lead to sub-optimal image reconstruction and decreased ability to detect uptake of PET contrast media in lung tumors. Inadequate or incorrect attenuation density correction can also result in image artifacts that may obscure pulmonary nodules.